Corrosion rates of electrodeposited Zn and Zn-Sn (20-30m%) coatings are compared to hot dipped ones and pure Zn is aerated/deaerated 0,5 mol.dm-3 sodium sulphate solution. Results of electrochemical impedance measurements performed on Zn-Sn coating deposited from a slightly acidic bath containing sulphate ions have revealed the merit ot the passivity of this alloy. Corrosion potential of the alloy remains close to that of pure Zn, while a compact non-stoichiometric Zn/ZnO and Sn/SnO/SnO2 layer forms and due to its weakly degenerated n-type semiconductance the rate of the cathodic processes are markedly reduced. From dependence of capacity on electrode potential the electron density in the oxide film (1019-1020 cm-3) was determined. The zinc oxide films are more sensitive to local damage in the presence of sulphate ions. The dark yellow chromate layer on Zn-Sn coating has better corrosion protection than the iridescent yellow chromate layer on Zn coating.
|Translated title of the contribution||A comparative corrosion study of zinc and zinc-tin galvanic coatings by method of electrochemical impedance spectroscopy|
|Number of pages||7|
|Publication status||Published - Jan 1 2000|
ASJC Scopus subject areas
- Chemical Engineering(all)
- Surfaces, Coatings and Films
- Materials Chemistry